This invention relates generally to footwear, and in particular to a liner for cushioning a foot inside the footwear wherein the liner visually indicates whether the liner is effectively cushioning the foot during use.
When walking or running, the heel of the foot generally strikes the ground first during each gait cycle. The foot then pivots on the heel until the lateral (outside) part of the forefoot contacts the ground. At this point, the foot rolls inward to a supinated position, and then rapidly outward to a neutral position in which the bottom of the heel and the metatarsal heads of the forefoot contact the ground. Next, the foot rolls from the neutral position back to a supinated position prior to the propulsive phase of the gait cycle. During the propulsive phase of the gait cycle, the foot pivots upward on the forefoot as the toes push off the ground to propel the foot forward and assist the corresponding leg in pulling the foot toward the next step.
In view of the foregoing, it will be observed that various parts of the foot impact the sole of footwear during various portions of each gait cycle. To cushion the foot, the soles and sockliners of footwear are frequently made of compliant materials. Further, to enable the upper to conform to the foot, compliant materials are frequently used inside the uppers of footwear and these materials also help to cushion the foot from impacts. However, over time and through use, the compliant materials gradually lose their resilience so they have a reduced ability to protect against impact and to conform to the foot. When this happens, the footwear and/or the removable liners must be replaced to avoid injury to the foot due to impact or improper fit.